NeoTrace is a really cool Windows program (trial version available at WWW.NEOTRACE.COM) which, when given an IP address or domain name, will plot graphically on a world map the route that internet data packets have taken to get from you to them, as well as all available information about the various machines along the path.

It is invaluable for finding out all sorts of interesting geographical information about the net, other users, web servers, and so on. Combines many of the features of a Reverse DNS search, a Whois lookup, a TraceRoute command, and more..